REPTILES. 251 



"Hence," says Professor Bell, "arises the circumstance that 

 these animals have what is called cold blood ; for, as it is from 

 respiration that the blood derives its heat and the temperature 

 of the body is thereby sustained, in animals which have more 

 perfect respiration, it follows that where this function is but 

 imperfectly performed, the animal heat, muscular force, and all 

 other functions dependent on respiration will be diminished."* 

 In the last class to which our attention was directed — that 

 of fishes — the circulation throughout life was suited to their 

 residence in water. The first we shall notice in the present 

 class are likewise fitted for aquatic respiration. We shall next 

 proceed to those which in their veiy eai'l}' stages breathe by 

 gills, but afterwards by lungs ; and thence pass on to those 

 which at all periods possess aerial respiration. 



Oedee I.— amphibia. 



"The sT\-imming Frog, the Toad, the Tadpole, the Wall- Newt, and the 

 water." — Shaicsfeake. 



The Amphibious Eeptiles (order Batrachiaf of Cuvier) may 

 be separated into two divisions — those which possess both 

 lungs and giUs throughout the entire period of life, and those 

 which have gills in their young state, and acquire lungs as 

 they approach maturity.;]: The former group possesses some 

 animals of very singular structure and habits ; as the Proteus, 

 which inhabits subterranean lakes in the Tyrol, the Axolotl 



• History of British Reptiles — Yan Voorst; another of that attractive 

 series of works illustrative of the natural history of these countries. In the 

 opinion of the learned author of that work, the structural peculiarities of the 

 Amphibia are such as to justify their being regarded as a distinct class, in- 

 stead of being merely- ranked as one of the orders in the class Reptilia. 

 Mr. Jcn\-ns has thus arranged them in his " Manual." 



f From the Greek word signifying a frof/ (Lat. Batrachus). The term 

 Batrachian means, therefore, a frog-like animal. 



X Those in which the gills are permanent are termed Perennibran- 

 CHiATE (Latui, branchirr, the gUls, and perennis, permanent, lasting, staying 

 all the year round). Those in which the branchiae disappear, are termed 

 CADrciBRA>'CuiATE, the word caducus meaning perishable, falling of 

 itself, &c. 



